Some communication systems allow the user of a terminal, such as a personal computer or mobile terminal, to conduct voice or video calls over a packet-based computer network such as the Internet. Such communication systems include voice or video over internet protocol (VoIP) systems. These systems are beneficial to the user as they are often of significantly lower cost than conventional fixed-line or mobile networks. This may particularly be the case for long-distance communication. To use a VoIP system, the user installs and executes client software on their terminal. The client software sets up the VoIP connections as well as providing other functions such as registration and authentication. In addition to voice communication, the client may also set up connections for other communication media such as instant messaging (“IM”), SMS messaging, file transfer and/or voicemail.
One type of communication system for packet-based communication uses a peer-to-peer (“P2P”) topology. To enable access to a peer-to-peer system, a user executes P2P client software supplied by a P2P software provider on their terminal, and registers with the P2P system. When the user registers with the P2P system, the client software is provided with a digital certificate from a server. This may be referred to as a “user identity certificate” (UIC). Once the client software has been provided with the certificate, then calls or other communication connections can subsequently be set up and routed between end-users (“peers”) of the P2P system without the further use of a server in the call set-up. Instead, the client looks up the required IP addresses from information distributed amongst the P2P client software on other end-users' terminals within the P2P system. That is, the address look-up list is distributed amongst the peers themselves. Once the IP address of a callee's terminal has thus been determined, the caller's P2P client software then exchanges UIC certificates with the callee's P2P client software. The exchange of these digital certificates between users provides proof of the users' identities and that they are suitably authorised and authenticated in the P2P system. Therefore the presentation of digital certificates provides trust in the identity of the users.
It is therefore a characteristic of peer-to-peer communication that, once registered, the users can set up their own communication routes through the P2P system in at least a partially decentralized manner based on distributed address look-up and/or the exchange of one or more digital certificates, without using a server for those purposes. Further details of an example P2P system are disclosed in WO 2005/008524 and WO 2005/009019.
VoIP or other packet-based communications can also be implemented using non-P2P systems that do use centralized call set-up and/or authentication, e.g. via a server.
In a communication system it is often useful for the client application to maintain a log of past communication events. This helps improve operation of the network by facilitating continuity in threads of communication. For example a thread could comprise a chain of related communications such as calls or IM sessions between the same two or more users. If one or more communications are postponed or missed, then the log will enable those communications to be more readily identified and therefore the thread of communication can be more efficiently recovered by a user at a later date.
A conventional communication client application provides the user with the ability to retrieve a log of calls that they have made, received or missed. The log may also record other communication events such as IM sessions or voicemail messages. These logs comprise a list of communication events which are typically sorted chronologically and which record the type of call or event that took place, who the call was with, and the time of the event.